Michaels
membrane separation device



Oct. 11, 1966 A. s. MICHAELS 26,097

MEMBRANE SEPARATION zmvzcm Original Filed Sept. 28, 1962 5 Sheets-Sheetl 4 1 FIG. I F G- 2 ""IUH HIIIIIIHHHH" "mull! lllil I8 FIG. 3 l4 l8 HG.4 l4 ENTOR. ALAN S. HAELS BY 15 a m ATTORNEYS A. s. MICHAELS Re. 26,097

MEMBRANE SEPARATION DEVICE Original Filed Sept. 28. 1962 Oct. 11, 1966 3Sheets-Sheet 2 IIIIIIIA'IIIIIIIIA INVENTOR. ALAN S. MICHAELS BY ff mny,Jmae yim ATTORNEYS Oct. 11, 1966 A. s. MICHAELS 25,097

MEMBRANE SEPARATION DEVICE Original Filed Sept. 28, 1962 3 Sheets-Sheet3 "FIG. l0

INVENTOR ALAN S. MICHAELS BY fi m mu 14 44 ATTORNEYS United StatesPatent 26,097 MEMBRANE SEPARATION DEVICE Alan S. Michaels, Lexington,Mass., assignor to Amicon Corporation, Cambridge, Mass, a corporation ofMassachusetts Original No. 3,173,867, dated Mar. 16, 1965, Ser. No.

226,917, Sept. 28, 1962. Application for reissue Dec.

17, 1965, Ser. No. 517,165

7 Claims. (Cl. 210-321) Matter enclosed in heavy brackets II] appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to devices for carrying out dialysis and othermembrane separations in which a fluid is brought into contact with onesurface of a membrane so that a component of the fluid will pass throughthe membrane into another fluid.

There have been developed numerous processes and systems for theseparation or purification of solutions and other liquid and gaseousmixtures by means of the selective transmission of material through amembrane from one fluid to another. Ideally the apparatus for suchprocesses should provide a large membrane contact area per unit volumeof space occupied, and as best results are attained through thin,structurally weak membrane materials, adequate support for the membraneagainst deformation or rupture by hydraulic pressure, or thermal ormechanical shock should be provided. In addition the fluid streams incontact with the membrane should be very thin, preferably of a thicknessof the same order as the membrane itself, in order to minimizecounter-diffusion caused by the concentration gradient which resultsfrom depletion of the film of fluid at the membrane-fluid interface. Theapparatus should also be constructed so that flow conditions may bevaried and ideally the construction should be simple, inexpensive andreliable.

Devices heretofore available for carrying out membrane separations havegenerally utilized membrane stacks, or sacks, or coiled tubes ofmembrane materials, and have not fulfilled all the requirementsdiscussed above. In particular no device heretofore available combineshigh membrane area per unit volume in a compact unit capable ofoperating at high pressures at greatly varying flow rates and in asimple and inexpensive construction.

It has been proposed to construct a membrane separation cell in the formof a spirally wound assembly in which the membrane separates one fluidflow chamber from another, but no device of this type is yetcommercially available, and as far as we are aware none has beensuccessful. In connection with the efforts leading to the presentinvention, it is noteworthy that combining a membrane with the otherelements to form a spiral assembly presents numerous problems. Oneelement of the spiral is inherently longer than the other, and thisdifference in length must be accommodated. In addition the connectionsnecessary for properly feeding the two fluids to their respectivecompartments are not easily provided.

The membrane separation cell of this invention is formed of one or moreelongated cell units wound as a spiral about a perforated hollow innercore. The basic cell unit consists of an elongated base strip to themargins of which the edges of the separation membrane are attached; thespace between the base strip and membrane defining one (the primary)cell region. This unit is wound upon itself with the turns spaced fromeach other so that the space between the turns defines the other (thesecondary) cell region. Fluid flow through the primary cell region isprovided for by connecting the inner end of the basic cell unit to theinner core so that it serves as a conduit leading to the inner end ofthe primary cell region.

Re. 26,097 Reissued Oct. 11, 1966 "ice The outer end discharges into thespace surrounding the wound assembly, which is confined within thehousing for the unit, and a conduit through the housing provides a fluidconnection to the outer end.

In the secondary cell region the fluid is caused to flow in thedirection parallel to the spiral axis, between the ends of the housingin which suitable conduits are provided. The primary and secondary cellsare separated by an application of a sealant composition to formappropriate gaskets in the region where the two areas would meet.

Basically the present invention centers about the use of a thin backingmember, one side of which is formed with a surface configuration whichin conjunction with an overlying membrane forms a longitudinal flow pathin the primary cell region through which one fluid may be passed, whilethe other surface is provided with a configuration which results in atransverse flow-path in the secondary cell region which lies betweensuccessive turns of the spiral.

For a more complete understanding of this invention reference is made tothe following description of what is now considered to be the preferredembodiment of this invention, which is set forth for purposes ofillustration and is shown in the accompanying drawings in which:

FIG. 1 is a fragmentary plan view of one side of the interleaving basemember illustrating the surface formed with longitudinal channels;

FIG. 2 is a fragmentary view of the other side of the interleaving basemember shown in FIG. 1, showing the surface formed with transversechannels;

FIG. 3 is a transverse section through the interleaving base member,taken at 3--3 in FIG. 1;

FIG. 4 is a fragmentary longitudinal section of the interleaving basemember, taken at 44 in FIG. 1;

FIG. 5 is a transverse section of the membrane-base member laminateshowing the membrane assembled with the interleaving base member;

FIG. 6 is an isometric view showing a partial turn of the membrane-basemember laminate wound on a hollow perforated feed core, at the start ofthe winding operation in which the spiral cell is formed;

FIG. 7 is an isometric view of the completed cell wind- 8;

FIG. 8 is an axial cross-section taken through an assembled cell in itscasing;

FIG. 9 is a radial section of the cell taken at 99 in FIG. 8;

FIG. 10 is a radial section showing the end of the spiral core taken at10-10 in FIG. 8;

FIG. 11 is a fragmentary view showing the ends of overlapping adjacentturns in the cell winding with arrows representing the transverse flowof fluid.

The membrane separation cell of this invention is formed by winding amembrane 10 and an elongated base strip 12 to one side of which theedges of the membrane are secured. The base strip 12 is a long strip ofthin material having a surface configuration in a central band on theside facing the membrane which with the membrane defines a longitudinalflow path. As illustrated in FIGS. l5 this configuration may take theform of longi tudinal shallow grooves, or any other form which willsupport the membrane and at the same time permit a fluid to flowlongitudinally between the base strip 12 and membrane 10.

The other side of the base strip 10 is provided with a surfaceconfiguration which, when in contact with the other side of themembrane, will define a transverse flowpath; as illustrated in FIGS. i-5this may take the form of transverse grooves.

The base strip 12 is formed with marginal areas 18 on each side of thecentral band carrying the grooves 14 and 16, to which the edges of themembrane 10 are secured The marginal portions 18 are of reducedthickness and are each provided with opposed creasing grooves 19, atwhich each margin is folded around the overlying edge of the membraneand adhesively bonded thereto, as shown in FIG. 5.

The membrane 10 and the base strip 12 thus together define alongitudinal channel (primary cell region) through which one of thefluids in a membrane separation system may be passed. The other fluid iscaused to flow on the outside of the assembly, in the transversechannels between the transverse groove 16 and the membrane 10 lying incontact therewith when the assembly is wound into a spiral. A portion ofthe successive turns defining the transverse flow-path (secondary cellregion) is shown in FIG. 11.

In forming the spiral cell the membrane 10 and base member 12 assemblyare wrapped on a hollow core 20 having perforations 21 through which onefluid may be introduced into or removed from the primary cell region. Inwrapping the base member 12 and membrane 10 the membrane 10 ispreferably located on the outside of the turns, and when wound will beof relatively longer length than the base member 12. The difference inlength may be accommodated by utilizing a slow curing viscous liquidadhesive, e.g. an epoxy resin, or isocyanate resin, between the edges ofthe membrane and the base member margins 18, so that relative slippagecan occur, or by forming base member 12 of a relatively compressiblematerial, or the membrane 10 of a relatively elastic material.Alternatively the membrane 10 and base member 12 may be fed separatelyinto the roll and combined just prior to their being wound onto theroll, whereby different lengths of these materials may be supplied tothe spiral.

To separate the two flow paths, a layer of adhesive is applied betweenthe bottom or back of the base strip and the membrane 10 at the end ofthe first turn, as illustreated at 22 in FIG. 9, and also between thesetwo members at the end of the last turn as illustrated at 23 in FIG. 9.In this manner the fluid flowing in the longitudinal path is preventedfrom entering at the ends of the wound assembly into the secondary cellregion between the membrane and back side of the base strip.

The rolled assembly is arranged for the introduction of fluids to theflow-paths by placing it in a cylindrical housing 24, preferably afterapplying an outer layer of porous material 26, erg gauze, felt orscreen, to serve as an outer support which will permit the flow of fluidin the area immediately surrounding the assembly. The rolled assemblywith the outer permeable wrapping 26 is contained within a cylindricalshell 24 which is provided with an outlet 28 through which fluidconnection is made with the outer end of the primary cell region.

After the wound assembly is placed within the shell 24 coatings 30 and31 of a viscous, film forming, cement are applied about the edges of thefirst turn and last turn to provide a seal between the primary andsecondary cell regions where they would otherwise be in communication,ss shown in FIGS. 8 and 10.

End caps 32, each having tightly fitting collars 33 surrounding thecentral core 20 fit over the ends of the shell 24, and are held in placeby plates 34, which are held together by longitudinal bolts 35. Collaredports 36 in the end caps provide for the introduction of fluid to theends of the rolled assembly.

In the illustrated embodiment O-rings 38 are provided between the sideflanges 39 of each end cap and the ends of the shell 24, and similarlyO-rings 40 lie between the central flanges 33 and the central tube 20.

In operation, one of the fluids is introduced into the central tube 20and removed through the outlet 28 after having flowed in a radial spiralpath the length of the longitudinal flow-path. The other fluid isintroduced into one of the collared openings 36 in one end cap fromwhere it flows generally parallel to the spiral axis along thetransverse flow-paths defined between the successive turns, and then outthrough the collared opening 36 in the opposite end cap.

In the preferred design of the membrane separation device embodying thisinvention, the base strip 12 is preferably a thin flexible material,e.g., a plastic such as polyethylene, polypropylene, polyvinyl chloride,cellulose acetate, or a metal such as aluminum, stainless steel, orcopper, and may itself constitute a membrane material. Its surfaceconfigurations defining the longitudinal and transverse flow-paths,should define a path which is thin relative to the membrane, e.g.,between 0.5 and ten onethousandths of an inch, and the base memberitself should also be as thin as possible in order to facilitate windingand to provide for as great as possible a utilization of the space forthe membrane material.

An important aspect of the construction of the base strip 12 is thatwhen it is wound up with the membrane successive turns of the base stripcome in contact with opposite sides of the membrane, as shown in FIG.11. This contact is assured by making the central band of the base strip12 thicker than the margins so that the central portion, not themargins, determines the spacing of the turns, and so that the margins donot obstruct the flow of fluid to the secondary cell region.

The separation membrane may be any of numerous sheet materials useful inmembrane separation systems such as cellulose acetate, cellophane,polyethylene or other synthetic or natural sheet materials.

From the foregoing description it will be seen that a high contact areaof membrane surface is provided. As an example if the base strip is 0.05inch thick, the membrane 0.001 inch thick and the grooves 0.010 inchdeep, one hundred square inches of membrane per cubic inch of fluidcontent and about 20 square inches of area per cubic inch of total unitvolume are provided. A unit with a volumetric capacity of one quartwould provide for a total membrane area of over forty square feet.

In addition to the large area of surface the extreme thinness of the ofthe fluid layers in the primary and secondary cell regions results in avery high separation efficiency because counter diffusion of thematerial being transferred is greatly reduced.

The spiral arrangement of the system in a cylindrical housing permitsoperation at high pressures, since all fluids are confined within thehousing and end caps, which can be made as strong as desired. If bothfluids are under the same pressure, no pressure differential across themembrane is created.

Membrane separation systems embodying this invention are accordinglyuseful for many purposes, such as dialysis or ultrafiltration includingservice as a hemodialyzer (artiflcial kidney), the removal of salt fromseawater, the removal of liquid components by pervaporation, and as apermeator for separating components of gaseous mixtures.

Although this invention has been described with specific reference tothe illustrated preferred embodiment, it is apparent that numerousmodifications may be made by those skilled in the art and familiar withthis disclosure. Different precise base strip constructions may beemployed, as well as the manner of assembling the base strip andmembrane. Also several base strip-and-membrane assemblies may be woundtogether on the central core to provide parallel primary cell regions,and several cornplete membrane separation units may be arranged inseries or in parallel, or partly in series and partly in parallel toprovide a great variety of types of arrangements for specific purposes.

Having thus disclosed my invention, I claim and desire to secure byLetters Patent:

1. A membrane separation device comprising an elongated base striphaving spacing means on both surfaces thereof and an overlying membranehaving their longitudinal margins secured together and defining aprimary cell region between them having a thickness between fivetenthsand ten one-thousandths of an inch, said membrane and base strip beingtogether wound into a spiral assembly to define a secondary cell regionbetween the turns of the spiral, said secondary cell region having athickness between five-tenths and ten one-thousandths of an inch, aconduit extending to the center of the spiral and communicating with theinner end of the primary cell region, a cylindrical housing surroundingthe spiral and communicating with the outer end of the primary cellregion, end caps at the opposite ends of the housing communicating withopposite sides of the secondary cell region, sealing means at theopposite sides of the spiral adjacent to the conduit and covering theedges of the innermost turn of the spiral, and sealing means at theopposite sides of the spiral adjacent to the housing and covering theedges of the outermost turn of the spiral, said sealing means separatingthe primary cell region from the secondary cell region.

2. A membrane separation device comprising a spirally wound assemblydefining at least two fluid flow paths; said assembly including anelongated flexible base strip having on one surface a reliefconfiguration defining a longitudinal fiow path and on the other surfacea relief configuration defining a transverse flow path, and a separationmembrane interwound with said base strip and joined thereto at themargins on said one surface thereby forming a primary cell region,having a thickness between five-tenths and ten one-thousandths of aninch, the turns of said assembly establishing a secondary cell regiondefined between said other surface of said base strip and the separationmembrane of the adjacent turn; said secondary cell region having athickness between five-tenths and ten onethousandths of an inch, conduitmeans communicating with the inner end of said primary cell region, ahousing surrounding said assembly and communicating with the outer endof said primary cell region, and end caps on the ends of said housingcommunicating with opposite ends of said secondary cell region.

3. A membrane separation device comprising a spirally wound assemblydefining at least two fluid flow paths, said assembly including anelongated flexible base strip having an inner band of relatively greaterthickness extending longitudinally between opposed margins of relativelylesser thickness, one surface of said strip having a reliefconfiguration defining a longitudinal flow path and the other surfacehaving a relief configuration defining a transverse flow path, aseparation membrane interwound with said strip and joined to the marginson said one surface thereby forming a primary cell region having athickness between five-tenths and ten one-thousandths of an inch, thetums of said assembly establishing a secondary cell region definedbetween said other surface of said base strip and the separationmembrane of the adjacent turn, said secondary cell region having athickness between five-tenths and ten one-thousandths of an inch,conduit means communicating with the ends of said primary cell region,and conduit means communicating with the ends of said secondary cellregion.

4. The membrane separation device defined by claim 3 wherein the marginsof the base strip are less than half the thickness of the inner band andare folded over the edges of the separation membrane.

5. A membrane separation device comprising a spirally wound assemblydefining at least two fluid flow paths, said assembly including anelongated flexible base strip having an inner band of relatively greaterthickness extending longitudinally between opposed margins of relativelylesser thickness, one surface of said strip having a reliefconfiguration defining a longitudinal flow path and the other surfacehaving a relief configuration defining a transverse flow path, aseparation membrane interwound with said strip and joined to the marginson said one surface thereby forming a primary cell region having athickness between fivetenths and ten one-thousandths of an inch, the

turns of said assembly establishing a secondary cell region definedbetween said other surface of said base strip and the separationmembrane of the adjacent turn, said sec- 5 ondary cell region having athickness between five-tenths and ten one-thousandths of an inch,conduit means communicating with the ends of said primary cell region, ahousing surrounding said assembly and communicating with the outer endof said primary cell region, and end caps on the ends of said housingcommunicating with opposite ends of said secondary cell region.

6. A membrane separation device comprising a spirally wound assemblydefining at least two fluid flow paths, said assembly including anelongated flexible base strip having an inner band of relatively greaterthickness extending longitudinally between opposed margins of relativelylesser thickness, one surface of said strip having a reliefconfiguration defining a longitudinal flow path and the other surfacehaving a relief configuration defining a transverse flow path, aseparation membrane interwound with said strip and joined to the marginson said one surface thereby forming a primary cell region having athickness between five-tenths and ten one-thousandths of an inch, theturns of said assembly establishing a secondary cell region definedbetween said other surface of said base strip and the separationmembrane of the adjacent turn, said secondary cell region having athickness between five-tenths and ten one-thousandth of an inch, aconduit extending to the center of the spiral and communicating with theinner end of the primary cell region, a cylindrical housing surroundingthe spiral and communicating with the outer end of the primary cellregion, end caps at the opposite ends of the housing communicating withopposite sides of the secondary cell region, sealing means at theopposite sides of the spiral adjacent-to the conduit and covering theedges of the innermost turn of the spiral, and sealing means at theopposite sides of the spiral adjacent to the housing and covering theedges of the outermost turn of the spiral, said sealing means separatingthe primary 40 cell region from the secondary cell region.

7. A membrane separation device comprising a spirally wound assemblyincluding an elongated base strip having on both surfaces thereof aplumlily of grooves, the grooves on one surface extending longitudinallyand on the other surface extending transversely, and a membraneinterwound with said base strip overlying said one surface and sealedthereto along their longitudinal margins thereby forming a primary cellregion at said one surface and a secondary cell region a! said othersurface, at least one conduit communicating with at least one end of oneof said cell regions, and conduits communicating with both ends of theother of said cell regions.

References Cited by the Examiner The following references, cited by theExaminer, are of record in the patented file of this patent or theoriginal patent.

UNITED STATES PATENTS REUBEN FRIEDMAN, Primary Examiner.

F. SPEAR, Assistant Examiner.

